Insulation testing system



SePt- 29, 1931- l l.. w. BREHMAN 1,824,802

INSULATION TESTING SYSTEM Filed Jan. 22, -1929 WHL.

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. invention relates to systems fortestving, the ,conductors of a cable in order -to detect the leakage. v ,v I In accorda'mze with this invention an arrangement provided vfontesting two or 'more' conductors, composing one or.. more cables, to determine whether a leak has developed or whether the insulation resistance l'lehas decreased so as torender the system` suzs.-

ceptible to failure for practical purposes.

A'vacuum tube system acting as a detector l is employed in connection with a sensitive relay and analarmcircuit for determining 1l when trouble may develop, due to low insulation or high leakage, in two or more of the conductors forming one or more lines.. vThe sensitive relay is connected in the output circuit of the vacuum tube system and controls 2 the operationof the alarm circuit, an alarm being sounded whenever the insulation propp erty of two or more ofthe conductors drops ,below a predetermined level.

It is one of the objects of this invention to u. provide a system for indicating poor insulation in a pair of conductorsof a line by couv pling these conductors to a vacuum tubesystem and a relay, so that when the insulation Aresistance of theconductors drops below a Jdefinite value the vacuum tube system will be energized sui'ciently to cause the operation of the relay.

While this invention will be pointed out with particularity in the appended claim, the

3.55 invention itself, both as to its further objects and features, will be better understood. from Athe detailed description hereinafterfollowing when read in connection with the accompanying drawings in which Figure 1 `shows -one embodiment of the invention and Fig. 2 a. modification ofthe arrangement shown in Fig. l1. I'

Referring to Fig. 1 of the drawings, a vacuum tube system is shown including a Ayacuum tube V having plate, filament and grid electrodes. The filament electrode is heated to incandescence by means ciabattery B1. The grid electrode is connected to 5o the filament electrode through a battery B,

presence of low `insulation or high connected to the filament electrode through and a resistance R1, battery B, being on such v 1 l a potential and so poled as to render thegrid electrode' highly negative with respect to the filament electrode. The plate e ectrode is the winding of a relay W and a batterynBs, battery B, being so poled and of such afvoltage as to render the plate electrode suitably positive with respect tothe lament electrode. Y

The armature of relay ,W is free to move between two contacts, designated 1 and .2, and

`is nor ally biased against `contact 2. In

series 'th the armature and contact 1 there '4 is a generatorv G and a ringer C. The generator G may be any source of alternating current, preferably one of low frequency, generating curre t of a frequency of, for example, twenty cyc es. The ringer C may be a bell ofthe type familiar in telephony or any device responsive to the current produced by generator G. It will be clearly understood that while a ringer C is shown 1n series with generator G, the ringer representing an audible indicating device, a visible indicating device of any well known type may be substituted therefor or used in addition thereto without departing from the spirit and scope of this invention.

A battery -B4 is shown connected .in series with resistance R1. This battery may be a source of current of high voltage of any well known type. Two conductors forming a line L are connected in series relationshipA with battery B4 and resistance R1. Conductors of a similar line L may be paralled with those of line L, and it willbe'understoodthat any number of lines may be similarly paral- Y leled within the scope of this invention. This invention will be described hereinafter with reference to only one of thelines, L.`

Under normal conditions the conductors forming line L representing an open circuit, and current cannot ,flow from battery: B4

through resistance R1L and over these `conduct'ors. Under such. conditions no voltage will b egenerated across the terminals ofv resist ance R1. The only voltage tending tobias the grid electrode o f vacuum tube V nega-v tivel will thatderived from battery Bz.

with respect to the filament electrode i Y In accordance with this invention the ing voltage of battery B or of any lent means, ismade so high as to t y impede the electronic emission from e filament 5 electrode to the plate electrode. Thus, the

' ilow of current `from battery B. thro h the winding of relay W will be o f a neg 'gible -magnitude. Itis necessary to employ a sensitive relay herein,.one which will not become' relzy gri electrode of vacuum tube V is ne tive with res ct to the filament electrode, y the voltage erived from' battery Bz. Relay must also be one which will become readlly operated when the negativity of the grid electrode is substantially reduced `or when the grid electrode is made somewhat positive with respect to the filament electrode.

When a condition of low insulation or high l leakage develops between the conductors of line L or in an pair of conductorsf. parallel thereto, the resistance between these conductors will not be infinite and therefore current will flow from battery B4 through resistance R1 and over these conductors. Resistance R.2 is one of finite magnitude, andrepresents that resistancel present when the insulationv between the conductors drops below a predetermined value or when the leakage increases to acorresponding extent. In fact, when a condition of low insulation or high leakage `'is develo d, the conductors of line L may be short-clrcuited, in eect In any event, current will ilowfrom battery B4 through resistanceR1 and over these conductors. f

Battery B4 is one of high voltage and is so poled as to render the left-hand terminal of resistance R1 considerabl more positive than the right-hand termina Accordingly, the voltage of battery B2 will be opposed by that produced by resistance R1. *..The voltage across resistance R1 may greatly decrease the negative bias of the grid electrode with respect to the filament electrodeso as to greatl reduce the impedance to electronic emisslon from the filament electrode to the plateelectrode, or that voltage across resistance R1 may be such as to evenirender the grid electrode somewhat positive with respect to the filament electrode. In either event, the electronic emission from the filament electrode to the plate electrode will be greatly increased, and the current from battery B3 through the windingV of relay W will be correspondingl increased. Inasmuch as relay W is one whic is quite sensitive, its'armature will be attracted and will close the associated contact 1. It is to be remembered that relay W Vis not s; caused .to operate until the voltage produced uiva-V W must remain unoperated while the tive Abias of the grid electrode in order to 'of' resistance R3.

by resistance R1 either partlyl or comIi-)letely overcomes that derived from'battery 4.

It will be apparent that after relay W has operated, current will flow from generator G through the ringer C, causing an audible signal. If a condition of low insulation or. high leakage develops in "anyof the other airs of conductors paralleling those of line E, relay NV will operate and cause a similar audible signal at -ringer C.

It is to be understood that while the arrangement of Fig. 1 is one inA which the grid electrode of a vacuum tube system is made negative with respect to the filament electrode to prevent theilow of current throughthe winding of relay W under normal conditions, this grid electrode may be onl'y slightly nega-1 tive or somewhat positive with respect to the filament electrode, so that substantial current may flow through the winding of relay W under normal conditions.- In the latter V event battery B4 must be so poled as to produce a voltage across resistance R1 to overcome the slightly negative orsomewhat posirender it highly negative and to cause relay W to become released. l

Fig. 2 shows a modification of the arrangement of Fig. 1. Here battery B5 is connected in series with a' resistance R3 and the 9i filament electrode of the vacuumtube V. A contact may be moved across resistance R, and this contact is connected to the grid electrode through a resistance R4'. The flow of current frombattery B5 causes a drop in voltage across the terminals of resistance R3, and by the manipulation of the movable contact any portion of this voltage may be obtained tobias the grid electrode of vacuum tube V negatively with respect to the filament electrode to any desired extent. Under normal conditions no current iiows through resistance R4.

In the arrangement of Fig. 2 the line L is connected in series with the high voltage battery B4, resistance R4 and a portion of resistance R3 through the inner contacts of a keyA K. The object in providing the variable corntact on resistance R, is to permit an accurate adjustment to be made of the magnitude of the bias for the grid electrode of the vacuum tube in order that the tube may operate at the proper point in its characteristic curve and prevent the operation of relay W under normal conditions. By operating key K, a re- 120 sistanceR, of a definite andpredetermined value will be connected in series relationship with battery B4, resistance R4 and a portion This resistance may have a value of, for exam le, three megohms, and may simulate'the resistance between the conductors of a good line, i. e., a line of high insulation and low leakage.

The alarm circuit which is under the control O relay W may be of a type somewhat Vi different from the one shown in the arrangement of Fig. 1. In Fig. 2 this alarm circuit includes a battery B, or other source of direct current, and a buzzer D or othervisible or audible indicating means responsive to the flow of direct current. It will be clearly understood that the alarm circuit shown in Fi 2 may be substituted forY` the one shown in i 1, and that the circuit shown in Fig. 1 may e ually well substituted for the one shown in ig. 2,- within the scope of this i11- .V tion.

ile this invention has been shown in certain particular arrangements merely for the purpose of illustration, it will be clearly understood that the general rinci'ples may be embodied in other and wi ely varied organizations without departing from the spirit of the invention and the scope of the ap nded claim. v

at is claimed is: An arrangment for indicating the presence Aof low insulation or high leakage in the conductors of a'line comprising a vacuum tube having plate, filament and grid electrodes, first, second and third batteries, first and second resistances, said first battery bein connected in series with the filament o said vacuum tube and said first resistance, said second resistance being con'- necte'd between the grid of said vacuum tube and a point movab e along said first resistance so that only a predetermined portion of said first resistance may be connected in series with the grid and filament electrodes of said vacuum tube, said second battery being connected in series with the line and that portion of the first resistance not connected in series with the grid and filament electrodes of said vacuum tube, and a relay havinA a winding connected in series with said third batte and the plate and filament electrodes of sai vacuum tube.

In testimony whereof, I have vsigned my .name to this specification this 17th day of January, 1929.

LUTHER W. BREHMAN. 

